This invention relates to a wind turbine. A wind turbine is a device for converting the energy of wind into mechanical rotary energy through the medium of a propeller type windwheel possessed of a plurality of rotor blades and further converting this mechanical rotary energy into electric energy by, for example, an electric generator. The operating condition of the wind turbine varies with the velocity of the wind. Specifically, the revolution number and torque of the windwheel increase and the loads such as the force of air and the centrifugal force which are exerted on the rotor blades are also increased in proportion as the velocity of wind increases. To fix the revolution number of the rotor blades, the motion of the blades is controlled by means of a variable pitch mechanism, for example. This control mechanism, however, fails to provide the expected control when the blades are exposed to a wind of unusually high velocity such as those encountered during a typhoon. Under the great pressure of the wind, the rotor blades and the rotation system of the motor may, in an extreme case, even break. The wind turbine, therefore, has an evident need of being provided with a safety measure to preclude breakage.
The rotor blades in the majority of the existing windwheels are made of glass fiber and aluminum. They must be given maintenance and inspection at fixed intervals of once at least several months. At times, they must be replaced. In some of the existing wind turbines, the propeller type windwheels are installed on towers which stand 50 to 60 meters from the ground level. The replacement of rotor blades and the maintenance and inspection given to the interior of the nacelle, accordingly, have entailed extremely dangerous work at great heights.
As one kind of the safety measure of the type mentioned above, there has been proposed a method which comprises making the tower on which the windwheel is mounted collapsible into an upper half and a lower half interconnected to each other through an intervening hinge and providing a weight at the lower end of the tower so that the whole tower can remain upright during normal operation of the wind turbine and enabling the upper half of the tower to be lowered to the horizontal about the hinge in the case of violent storm or other emergency or when maintenance and inspection are necessary. The upper half of the tower is held in the horizontal position until the emergency is over (Japanese Utility Model Publication No. 5044/1948).
In the method described above, since the rotor blades and the nacelle are fixed on the top of the tower, it is only when the height of the tower is not great that the rotor blades and the nacelle are brought down close to the ground after the upper half of the tower has been lowered. Since the upper half of the tower carrying the rotor blades is simply made horizontal, there still is a possibility of the rotor blades being broken by the force of a strong wind. In the case of a tower standing 50 to 90 m from the ground level and carrying thereon a large rotor having a diameter reaching even 100 m, it is extremely difficult to provide the tower in the middle thereof with a hinge. Even if the tower can be constructed so that the upper half thereof can be laid horizontally, the rotor blades and the nacelle are still 30 to 50 m above the ground level. Maintenance and inspection work is still dangerous. The replacement of the rotor is not easy to accomplish. Thus, the method has been applicable only to towers of small heights.